Force on a current currying wire in a magnetic field

In summary, the conversation discusses a positive reading on scales and the direction of force on a wire. It is determined that the wire is not attached to the scales but rather clamped at points D and E. The yoke attached to the scales is pushed down, suggesting a downward force on the wire. However, considering Newton's 3rd law, it is concluded that the wire is actually pushing the yoke down and the yoke is pushing the wire up. Removing the clamps holding the wire in place would result in the wire moving upwards.
  • #1
maxelcat
27
3

Homework Statement


This is a multi choice question from last years aqa a level. We know a positive reading is produced on the scales indicating something is pushing down on the scales.
Please see the picture.
stuck.jpg


Homework Equations


We know current direction, not B field.

The Attempt at a Solution


The positive reading on the scales suggests that the force on the wire is vertically down. Mark scheme says vertically up. We think Newton III is needed but not sure how it works.

Can anyone help explain why i is vertically up.
 

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  • #2
maxelcat said:
The positive reading on the scales suggests that the force on the wire is vertically down.
Is the wire attached to the scales?
 
  • #3
nope. = the wire is not attached to the scales, though it is clamped at points D and E.
 
  • #4
maxelcat said:
nope. = the wire is not attached to the scales, though it is clamped at points D and E.
Exactly. The yoke is what is attached to the scales. So rethink things with that in mind.
 
  • #5
so the yoke is pushed down. Which means the wire is pushing it down. So there must be a downward force on the wire...
 
  • #6
maxelcat said:
so the yoke is pushed down.
Yes.

maxelcat said:
Which means the wire is pushing it down.
Yes.

maxelcat said:
So there must be a downward force on the wire...
No. Consider Newton's 3rd law.
 
  • #7
well I think you are getting me to say that if the wire is pushing the yoke down then the yoke is pushing it up... but that doesn't make sense to me because I can't see how the interplay between the current and the mag field works. Suppose I then took away the clamps that are holding the wire DE in place and changed nothing else. The wire would move upwards - yes?
 
  • #8
maxelcat said:
well I think you are getting me to say that if the wire is pushing the yoke down then the yoke is pushing it up...
Sure. Newton's 3rd law in action. If A pushes B up, then B must push A down.

maxelcat said:
Suppose I then took away the clamps that are holding the wire DE in place and changed nothing else. The wire would move upwards - yes?
Yes.
 

What is the force on a current carrying wire in a magnetic field?

The force on a current carrying wire in a magnetic field is known as the Lorentz force, which is the combined force of electric and magnetic fields acting on a charged particle. This force is perpendicular to both the direction of the current and the magnetic field.

What is the direction of the force on a current carrying wire in a magnetic field?

The direction of the force can be determined using the right-hand rule, where the thumb points in the direction of the current, the index finger points in the direction of the magnetic field, and the middle finger points in the direction of the force.

How does the strength of the magnetic field affect the force on a current carrying wire?

The force on a current carrying wire is directly proportional to the strength of the magnetic field. This means that as the magnetic field increases, the force on the wire also increases. Similarly, if the magnetic field decreases, the force on the wire decreases.

How does the angle between the wire and the magnetic field affect the force?

The force on a current carrying wire is greatest when the wire is perpendicular to the magnetic field. As the angle between the wire and the magnetic field decreases, the force also decreases. When the wire is parallel to the magnetic field, there is no force exerted on the wire.

What are some real-life applications of the force on a current carrying wire in a magnetic field?

The force on a current carrying wire in a magnetic field is the principle behind many devices, such as electric motors, generators, and speakers. It is also used in particle accelerators and magnetic levitation systems. Understanding this force is crucial in the development of technology and advancements in various industries.

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